A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
The apparatus may be provided with an optical encoder measurement system including an irradiation system to direct an irradiation beam to a first scale for measuring a position of the first scale with respect to the optical encoder measurement system. The scale may for example be provided to a metrology frame while the optical encoder measurement system is provided to a substrate table so that the position of the substrate table with respect to the metrology frame can be measured. When the optical encoder system is provided to the substrate table, fibers/cables to the optical encoder system may move at high speed with the substrate table, deteriorating the dynamics and thermal behaviour of the substrate table.